Phenolic resins



Patented July 12, 1949 2,475,587 PHENOLIC Resins Y Howard L. Bender andAlford G. Farnham,

Bloomfield, N. J., assignors to Bakelite Corporation, a corporation ofNew Jersey No Drawing. Application February 27, 1945, Serial No. 580,072

'1 Claims. 1

This invention relates to phenolic resins and their preparation. In acopending application,

Serial No. 527,988, filed March 24, 1944, which matured into Patent No.2,464,207, there is disclosed the preparation of the sixhydroxy-hydroxy'-diphenyl-methanes that when isolated are crystalline;and the products by following the crystal-forming procedure can beobtained free from unreacted phenols, formaldehyde, catalysts,by-products, etc., that have been found to be sources of difliculty incontrolling the resinforming reactions and the resin properties and inavoiding discoloration, and the like. There is furtherdescribed thepreparation of resinous chain and cross-linked compounds from theisomers, and it is to the phase of resin-formation that the presentapplication is directed as a continuation-in-part of the aforesaidapplica tion.

In the direct reaction of phenol with formaldehyde, it has beendetermined that the substitution on the phenol ring tends to go first tothe ortho position to form a methylol group which in turn reacts with asecond phenol to give the diphenylol-methane; the next positions in theorder of reactivity on the rin are the para and then the remainingortho. It is possible by observing proper reaction conditions to thusobtain by the direct reaction of phenol and formaldehyde the threemethanes: o,o'-, 0,1)- and p,p'-diphenylol methanes. These methanes inturn can react with more formaldehyde, or they can react withformaldehyde and any other phenol with the separation of water, toproduce resins consisting of multiple orthoor paramethylene-chainedphenols; the open positions of the o,p and the pp isomer chains aregenerally ortho and occasionally para and of the 0,0 isomer chainsgenerally para, and these open positions are available for cross-linkagebetween chains to produce heat-reactive or hardtion of the crystallinefraction, 9. distillate passes over at 210-215 C. at 2 mm. absolutepressure that yields crystals from a solution in butanol that are the2,4 isomer. The 2,2 isomer formation is promoted by alkaline or neutralphenol-formaldehyde reaction conditions; the crystals can be obtainedfrom a xanthone fusion with caustic potash and hydrogenation. Thecrystals have the following structures and properties:

Melting point, C. Diortho (2,2) 119 Ortho-para (2,4') 120 Dipara (4,4')162 Solubility at 25 C. in benzene:

Gm./gm. benzene Rapidity of hardening of the crystals to infusibieresins:

Reaction with 2,2" 2,4 4,4 Phenol 15% hexa at 160 0 seconds 240 175 1651.5 mole formaldehyde and NaOH (1 at 100 C .mlnutes.. 31 55 120 1.5 moleformaldehyde and N H4011 (1%) at C 60.-.- 9 78 66 78 1.5 moleformaldehyde and ZnO (1%) at 100 C .d 6 62 58 18 The 2,2 crystalsdistill at 315320 C. with solne change to xanthene, the anhydride of theisomer,

- which proves the structure: the 2,4 crystals distill at about 330 C.with much decomposition and isomerization largely to the 4,4; and the4,4 crystals distill at about 336 C. with much decomposition andisomerization.

The above recited properties evidence considerable differences in theisomers dependent upon the position of the hydroxyl groups. Outstandingamong them are the differences in the speed of reaction to the infusibleresin state upon hardening with hexa (hexamethylenetetramine),' the 2,2isomer being four times as fast as the 2,4 isomer and three times asfast as the 4,4 isomer; by proper admixture of the isomers, it

oxide as the catalyst, however, the phenol-formaldehyde reaction at 100C. evidently goes through the rapid 2,2 stage to arrive at a hardeningspeed of more than three times that of either the 2,4 or the 4,4isomers.

The isolated crystals provide standards for checking resinous productsobtained in the condensations of phenols and aldehydes or ketones; andresins made from the crystals insure absence of contaminants and exactduplication in the resin properties of different batches. In theproduction of resins, however, it is not usual or necessary to isolatethe crystals and then proceed with further reaction of crystals withformaldehyde to form resinous chain structures; after the controllingconditions have been determined, a resin chain formation of anyparticular type can be brought about by continuing the initialcondensation to a resin stage under conditions yieldi i 3" our omnolariy well into a chain formation due,it is believed, to thehydrogen-bonding energy (z) of the hydroxyl groups to leave open onlythe relatively sluggish second ortho positions (of the three positionsin order of reactivity, ortho, para and ortho to the hydroxyls) inconformance to the structural formula: 1

as the 4,4, and on test it was found to be slower in reaction withformaldehyde; this is indicated by the formula:

The 2,2 isomer in the reaction with formaldehyde shows a still moredifiicult condition for forming hydrogen-bonded rings; but it does leaveopen in the chain the much more active positions that are para (p) tothe hydroxyls to give OHzHO a markedly increased speed in subsequenthard- (n) i onnzrov 011:110

ing the fusible or novolak type resin, such as the ening (cross-linking)reactions as shown by the formula:

In other words, the 4,4 isomer is fastest in the condensation withformaldehyde into a chain structure, but the 2,2 chain structure is byfar the speediest in cross-linking by a hardening agent; thehardening-reaction speeds of the crystalline isomers as given in theforegoing table support the structural explanation.

It has been determined that a convenient indicator of the structures isthat of bromination.

By reacting phenol with an excess of potassium bromide-bromate for 2hours at 50 C. it was found that 4.65 bromine atoms unite instead of theusual 3 atoms (tribromphenol test). Pure reference materialsbenzene,diphenyl, diphenyl-methane and orthohydroxy-diphenyl-methane were usedfor establishing bromine values for the phenyl ring, the bondingmethylenes and the ortho-mono-hydroxy-phenyl ring; actual bromine valuesunder the same conditions were also obtained for the diphenylol-methanesand of the chain-structure resins made from them by reaction withformaldehyde. As a result a phenol resin can be brominated and from therate of bromination an average value can be obtained that points to itsortho or para structure or admixture proportions. For pure crystallinecompounds the data enables a calculation of the bromination per mole andfor all its parts, such as the para-hydroxy-phenyl ring; but for resinsi0 UOH: 0H:H0

The 2,4 isomer cannot hydrogen-bond as well "ultimate number 2000Xmolecular weight TABLE I Bromination values Ultimate" Gram AtomsSubstance gigg ing per Mole Phenol 98. s 4. 65 ParabenzylphenoL. 59. 55. 47 Orthobenzylphenol. 51. 2 4. 71 Diphenyl-methane. 25. 3 2. 13Benzene 4. 6 0.18 Diphenyl 14. 1 1.09 2, 2-Diphenylol-metbane (crystels)64. 0 6. 40 2, 4'-Diphcnylol-methane EcrystalsLm 86.0 8. 64 4,4'-Diphcnylol-mcthaue crystals).... 101.0 10.11 Resin (six rings) from2,2 51. 2 Resin Esix rings) from 2,4 55. 2 l Resin six rings) from 4,457. 4

"The uncertainty of the molecular weights of resins makes the gram atomsper mole of no significance.

From the bromination values then it appears that the 4,4 crystals havethe greatest reactivity with bromine, using approximately 4 atoms ofbromine per mole more than the 2,2 crystals in the same reacting timeand the 2,4 crystals are of intermediate reactivity. This is explainableon hydrogembonding taking place in the 2,2 isomer crystal, for thatinterferes with the bromination of the methylene group; the chaining ofthe 2,2 isomer cannot further influence this factor, since the isomeritself has all its possible hydrogen-bonding. In comparison the 4,4isomer crystal presents no possibility of hydrogen-bonding, and it istherefore active to bromine; the chaining of the 4,4 isomer, however,causes hydrogen-bonding and so a reduction in bromine- It has also beendetermined that the high crosslinking speeds are largely independent ofthe resin chain lengths; resins are thus obtainable that can pass from avery fluid or high flow condition to'infusible gels in a fraction of aminute at 160 C.

Factors governing the crystal structure and the novolak chain formationin the order of decreasing importance are: catalysts, temperature,contaminants, the measurable pH, ratio of reactants, reaction timeperiod, and exposure to air or oxygen.

In general a pH ranging from 4 to 7 is more favorable to structuralcontrol by means of catalysts and other conditions; such a pH value isobtained by adding a small amount (1%) ,of a base to aphenol-formaldehyde mixture, which without added catalyst and made ofpure reactants has a pH of about 4.5 The presence of impurities, such asammonium formats resulting from the presence of formic acid and itsreaction with ammonia, that do not register on the pH scale candrastically change the structure of the resin produced. One effect ofworking with a fairly neutral pH range is the slowness of the initialcondensation, and this permits a high temperature (above C.) that isfound to favor the 2,2 structure formation. Catalysts suitable for hightemperature reactions are zinc,

' magnesium and aluminum oxides that only become active at hightemperatures as slow resinification or chain-forming catalysts of themethanes initially formed; the critical temperature is about C. Incontrast, traces of acid, such as hydrochloric acid, favor the 4,4isomer formation and cause rapid reaction so that resin chainintermediates begin to fcrmby the time 100 C. is reached. With eitherbasic or acid catalysts, the 2,4 isomer is also formed, the percentagebeing dependent on conditions; for instance, reducing the reactiontemperature with basic catalysts increases the 2,4 formation, andlikewise ammonium and sodium hydroxides give increased yields of the 2,4isomer.

The presence of a large excess (15 to 30% or more) of the phenol overthe 1:1 molar ratio at the start of theinitial condensation of a phenol'and formaldehyde (or equivalent) is likewise an aid in directing theformation of the 2,2 structure. After the reaction has begun, the excessphenol can be, distilled off in condition for reuse. The reuse of thedistilled pure phenol greatly reduces the percentage of impurities addedby fresh charges of commercial phenol and formaldehyde, which impuritiesseem to favor the production of the 2,4 and 4,4 structures.

Substituted phenols in their reaction with formaldehyde are similarlysubject to control, the extent and rate of reactivity being modified bythe reactive positions available for reaction; for instance, meta-cresoland meta-xylenol, having the three reactive positions open, are muchlike phenol in reaction speed and the control of the resin chainstructure. Substituted aldehydes and ketones tend toward the formationof crystalline structures of the 4,4 type with acid catalysts and theseare hardenable with formaldehyde, paraformaldehyde, hexa, and similarhardening agents.

Under conditions of high reaction temperature and light metal oxidecatalyst most of the ortho positions on the phenyl rings are reacted inthe condensation and chain formation and the highly reactive parapositions left largely unreacted, in contrast to the novolakresin-forming processes heretofore followed (utilizing acid catalystsand low temperatures) that favor reaction at one of the ortho positionsand the para position to leave open the sluggish second ortho positionfor hardening resinification. The effect of this change is that, whilethe condensation and resin chain formation are relatively slow, thehardening or crosslinking in a molding operation is extremely rapid. Thehardening or gelation time is further subject to control by the amountof hardening agent, such as hexa, that is added to the novolak resinintermediate and by the temperature; for example, the time to gel at 150C. of an intermediate resin largely of the 2,2 structure dropped from 60seconds to about 30 seconds as the percentage of hexa added wasincreased fro 5 to 12%. i

The phenolic resin chain intermediates, particularly the 2,2 structuraltype, are somewhat diilicult to process by standard technical methods ofrolling the resin with wood flour and a low concentration of hexabetween hot rolls because the fluidity of the resin causes weakness inthe sheet; a maximum strength of the sheet was reached at about 10 to14% of hexa addition. The viscosity of molding material so produced ishigher than the usual run of material, the :molding pressure requiredincreasing with the hexa content up to about 14%, andadditional. hexaabove this amount then acts as a plasticizer to increase flow; mostly,however, the "increase in molding pressures is required because of thehigh speed of cure in order to close the mold rapidly and give fullpressure'on the material before the resin sets or loses flow. The speedof cure with hexa added is outstanding, a Rossi-Peakes flow testershowing the set time to be about 50 seconds at 150 C. when 10 to 12% ofhexa was used; bottle caps were cured in condition for discharge at 150C. in about 30 seconds with a 12% hexa content, and this is the shortestset-time commercially available so far for two-step resins -(i. e.novolak resins having hardener added). The hot discharge of the moldingmaterial also is accelerated by the hot-inflexibility and in thisrespect is superior to other phenolic ma-. terials. The combination offast cure and hotinflexibility has long been sought by the moldingindustry.

Example 1.-A high 2,2 novolak resin (about 60% 2,2 and 40% 2.4) was madeby charging .a still with Pounds Phenol 949.0 Formalin (37.5%formaldehyde) 126.5 Zinc oxide 3.2

The still contents were heated to reflux (113:- 115 C.) for 2.5 hoursand then to 160 C., allowing water to distill oil; it was held at 160/C. for 30 minutes, vacuum applied and the mass steamdistilled. In thedistillation about 70% of the phenol was recovered for reuse; and 276pounds of resin obtained with less than 0.5% of free phenol present. Theresin was tested by distillation and melting point and found to haveabout 60 per cent of the 2,2 structure, Upon mixing the resin with 55pounds of formalin and 2.7 pounds of zinc oxide and repeating thereaction, a novolak chain resin was obtained with a melting point of185-l95 F. (8590 C.) and it was very brittle on cooling; its brominationvalue was 52, and it hardened with 10-15% of hexa in 30-20 seconds orabout twice as fast as a typical commercial resin characterized as ahigh-speed hardening resin.

A molding material was made from by ball-milling the ingredients withthe exception of the wood flour; when thoroughly mixed the wood flourwas added and ball-milling was continued until the mixture had a uniformappearance; the mixture was then compounded on hot,

rolls (230260 F.) for about 1-1.5 minutes to flux and somewhat react theresin and hexa for improving flow and molding properties. The

sheets were cooled and ground to 16 mesh powder.

Example 2.-A resin high in the 4,4 structure was made by mixing phenol,100 pounds (1+ mole), aqueous formaldehyde (37.5%), 70 pounds (0.87mole), oxalic acid, 1 pound, and reacting for 4 hours at 100 0.; themass was dehydrated by heating to 140 C. The resin upon mixing with10-15% of hexa and heating to 160 C. became infusible in about 50-40seconds, and it had a bromination value of 62. A molding material wasmade from the resin as in the preceding example,

Comparative testswere made on the molding materials of Examples 1 and 2,a molding pressure of 2200 pounds per square inch and a mold temperatureof 320 F. being used; since the molded pieces were test pieces, theywere allowed to remain in the molds until fully cured. The

following properties were noted:

Example 3.-.A molding material was made from the 2,2 crystals byadmixing 15 per cent of hexa, and 42'parts of the mixture was ballmilledwith 58 parts of wood flour. The mixture required no hot rolling, sinceit had more than' enough flow for filling a mold; in fact it was sofree-flowing that merely contact pressure (1 to 10 pounds per squareinch) at molding temperature was suflicient for molding. The compositionof this example is differentiated in being free from impurities andagents affecting the molding process and properties in the moldedarticles; constancy in these respects is thereby assured.

For many molding purposes where the high speed of cross-linking thatcharacterizes the resin of Example 1 is not demanded, the resin isparticularly useful as an addition or component of the other one-stepand two-step phenolic resins for improving flow in a mold, increasingthe rate of hardening and for imparting hot-inflexibility; suchadditions are also useful in improving release from a mold as thisproperty also characterizes the resin of Example 1. Minor additions(25%) of the resin to a slow speed hardening resin have been found to soimprove the latter in these respects as to make it superior tocommercial one-step high speed resins.

What is claimed is:

1. Process of preparing fusible novolak resins from formaldehyde and aphenol having three reactive positions and selected from the groupconsisting of meta-cresol, meta-xylenol and phenol which comprisesreacting at refluxing temperatures an excess molar quantity of thephenol with formaldehyde at a pH between 4 and 7 and in the presence ofa metal oxide catalyst selected from the group consisting of zinc,magnesium and aluminum to form a mixture of diphenylol methanes,dehydrating the reaction mass, and then heating the diphenylol methanesto a temperature between and C. to chain the diphenylol methanes intoresinous intermediates characterized by open para positions inconsisting of meta-cresol, meta-xylenol and phenol which comprisesreacting at refluxing temperatures and at a pH between 4 and '7 anexcess molar quantity of the phenol with formaldehyde in the presence ofa metal oxidecataiyst selected from the group consisting of zinc,magnesium and aluminum to form a mixture of diphenylol methanes,dehydrating the "reaction mass, then heating the dlphenylol methanes toa temperature between 135 and 160 C. to chain the dlphenylol methanesinto resinous intermediates characterized by open para positions in thephenol rings for cross-linking with a hardening agent and thendistilling of! excess unreacted phenol.

3. Process of preparing fusible novolak resins from formaldehyde and aphenol having three reactive positions and selected from the groupconsisting of meta-cresoL'meta-xylenol and phenol which comprisesreacting at refluxing temperatures and at a pH between 4 and 7 an excessmolar quantity of the phenol with formaldehyde in the presence of ametal oxide catalyst seacting additional formaldehyde with the resinousintermediate in proportion to yield a novolak resin until a brittleresin at room temperature is formed.

4. Process of preparing a molding material which comprises reactingformaldehyde with a phenol having three reactive positions and selectedfrom the group consisting of meta-cresol, meta-xyienol and phenol whichcomprises reacting at a pH between 4 and 7 and at refluxing temperaturesan excess molar quantity of the phenol with formaldehyde in the presenceof a metal oxide catalyst selected from the group consisting of zinc,magnesium and aluminum to form a mixture of dlphenylol methanes,dehydrating the reaction mass. heating the dlphenylol methanes to atemperature between 135 and 160 C. to chain the dlphenylol methanes intoresinous intermediates characterized by open para positions in thephenol rings for crosslinking with a hardening agent, distilling on ex-10 cess unreacted phenol, reacting additional formaldehyde with theresinous intermediate in pro- P rtion to yield a novolak resin until abrittle resin at room temperature is obtained, admixing 5. A novolakreaction product of formaldehyde 4 and a phenol selected from the groupconsisting of phenol, meta-cresol, and meta-xylenol, said resin beingessentially methylene chained. diphenylol methanes, and a majorproportion of said methanes being 2,2'-diphenylol methane.

6. Phenol-formaldehyde novolak resin, being essentially methylenechained dlphenylol methanes, each phenylol group having at least oneactive position available for cross-linking by a methylene engenderinghardening agent, and a major proportion of said methanes being2,2'-hydroxy-hydroxy'-diphenyl methane, said resin being characterizedby an ultimate bromine number less than 55.

7. Molding material comprising molding material filler, a methyleneengendering hardening agent and a novolak resin of phenol andformaldehyde, said resin being essentially methylene chained diphenylolmethanes, each phenyloi group having at least one active positionavailable for cross-linking by a methylene engendering hardening agent,a major proportion of said methanes being o,o'-diphenyloi methane, andsaid resin having an ultimate bromine number less than 55.

- HOWARD L. BENDER.

ALI'ORD G..FARNHAM.

. REFERENCES CITED The following referenlces are of record in the fileof this patent:

Megson, Jour. Soc. Chem. Ind. (Apr. 1939), pages 131-139.

